Method of and apparatus for the detection of traces of chemical agents

ABSTRACT

THIS DISCLOSURE DEALS WITH THE DETECTION OF INTERMEDIATE AND HIGH MOLECULAR WEIGHT ORGANIC COMPOUNDS IN AQUEOUS ELECTROLYTIC SOLUTIONS, AS WELL AS OTHER TRACES OF CHEMICAL AGENTS, THROUGH MEASUREMENT OF THE RATE OF VARIATION IN OVERVOLTAGE AT ONE ELECTRODE IN AN ELECTROLYZING CIRCUIT.

June 22, 1971 w. JUDA ETAL 3,586,608

METHOD OF AND APPARATUS FOR THE DETECTION OF TRACES OF CHEMICAL AGENTS Filed Feb. 10, 1965 TRACE SOURCE ELECTROLYTE RESERVOlR DIFFERENTIAL VOLTAGE AMPUFIER AND RECORDER WALTER JUDA MARTIN S. FRANT, INVIZN'IURS BY m ATTORNEYS United I States Patent 3,586,608 METHOD OF AND APPARATUS FOR THE DETEC- TKON 0F TRACES OF CHEMICAL AGENTS Walter Juda, Lexington, and Martin S. Frant, Newton, Mass, assignors to Prototech Incorporated, Cambridge,

Mass.

Filed Feb. 10, 1965, Ser. No. 431,675 Int. Cl. G01n 27/46 US. Cl. 204-1 12 Claims ABSTRACT OF THE DISCLOSURE This disclosure deals with the detection of intermediate and high molecular weight organic compounds in aqueous electrolytic solutions, as well as other traces of chemical agents, through measurement of the rate of variation in overvoltage at one electrode in an electrolyzing circuit.

The present invention relates to methods of and apparatus for detecting traces of chemical agents and, more particularly, although not exclusively, to the detection of traces of intermediate and high molecular weight organic compounds in aqueous electrolytic solutions.

For many decades, observations have been made of the change in hydrogen overvoltage in electrolytic cells when additives have been introduced into the electrolyte. Measurements of the magnitude of overvoltage change have been effected in accordance with the teachings of Tafel, by permitting the system to reach stability and noting the overvoltage at, for example, the hydrogen electrode of electrolytic cells. In many cases, indeed, such variation of overvoltage has been considered detrimental, and complicated procedures have been introduced to avoid the same and to maintain the desired stability of the electrolytic solution.

In accordance with a feature of the present invention, on the other hand, beneficial use is made of such overvoltage variations with introduction of traces of impurities or other additives, generically referred to herein as chemical agents, and, in particular of a discovery underlying the present invention, that the rate of change of such overvoltage with time bears a relationship to the quantity of the trace agent and enables a rapid determination of such quantity without the time-consuming requirement for the reaching of a stable condition, as in accordance with the Tafel technique. It is, accordingly, an object of the invention to provide a new and improved method of and apparatus for detecting given traces of chemical agents in electrolytic media through utilization of the above-described discovery.

A further object is to provide a new and improved detection method and apparatus that is particularly, although not exclusively, advantageous in the detection of minute traces of intermediate and high molecular weight organic compounds in aqueous electrolytic solutions.

Still a further object is to provide for the detection of organic nitrogen-bearing compounds of intermediate and high molecular weight in electrolytic media.

Other and further objects will be explained hereinafter and will be more particularly delineated in the appended claims.

The invention will now be described in connection with the accompanying drawing, the single figure of which is a diagrammatic view of preferred apparatus for carrying out the method underlying the invention.

Referring to the drawing, an electrolytic cell is shown at 1 containing an anode electrode 3 and a cathode electrode 5 between which an electrolytic medium, such as an aqueous electrolyte solution, is fed at 7, the solution flowing through the cell 1 and out of an outlet 9 for an agitation purpose later explained. Traces of chemical agents, such as, for example, intermediate and high molecular weight organic compounds, may be added from a source 11 into the cell 1, as by the operation of a valve 13, or they may otherwise be inherently or otherwise present in the medium. The anode 3 is shown connected through a variable resistor R, an ammeter A and a switch S to, preferably, a direct current source B the negative terminal of which is connected to the cathode 5. When current is passed between the electrodes 3 and 5 through the elec trolytic medium therebetween within the cell 1, ions of the electrolytic solution are discharged at the electrodes; hydrogen being discharged at the cathode 5 in the case of, for example, an acid electrolytic medium. In the absence of traces of foreign chemical agents, a particular value of hydrogen overvoltage may be detected at the cathode 5 and recorded in any desired conventional detecting or recording apparatus 15.

As previously stated, when traces of the foreign chemical agents are introduced from the source 11, variations occur in the hydrogen overvoltage at the cathode 5 which will then be indicated by the apparatus 15 as, for example, on recording paper 15'. The term hydrogen overvoltage is used herein in its conventional meaning to represent the dilference between the potential of an electrode at which hydrogen is being evolved at a given current density and the potential of a standard (reversible) hydrogen electrode in the same solution.

Instead of the time-consuming operation of waiting for a stable reading of Tafel characteristic, the present invention utilizes the above-mentioned discovery, among others, to make a dynamic measurement of the variation of hydrogen overvoltage with time; i.e., the rate of hydrogen overvoltage variation which constitutes a measurement of the polarization rate at the cathode 5. As previously in timated, it has been found that the slope of the resulting variation of overvoltage with time (i.e., the rate) is a function of the quantity of the trace of added chemical agent introduced from the source 11, so that a dynamic and rapid measurement of the quantity of such trace is readily attainable in accordance with the invention.

As an illustration, extremely minute concentrations of organic amines have been thus detected with, in some cases, significant increases in hydrogen overvoltage producing stronger eifects, the higher the molecular Weight of the organic nitrogen-containing compounds. In the case of egg albumin traces, for example, with an 0.1 N H aqueous electrolytic medium, a drastic increase of over 300 mv. was observed over a 10 minute interval at 12.5 ma./cm. for a trace concentration of only 0.01 part per million of the egg albumin. A 50 mv. increase in hydrogen overvoltage was detected in 1 /2 minutes, as indicated by the slope of the curve C.

As another example, sensitive detection of the effects of organic traces on the overvoltage at relatively high current density was obtained with di-n-heptylamine, which produced an increase of 5 mv. with an increase in trace concentration from 10 molar to 1X lO- molar; the change occurring within 30 seconds. The anode and cathode electrodes in this case, as in the first example above, were platinum.

Similar behavior was observed for traces of dodecylbenzyldimethylammonium chloride (DBDA), but at lower concentrations and over a somewhat longer period; namely, 2 10' molar produced an immediate detectable shift in overvoltage with about seconds required for overvoltage stabilization.

The following table lists the overvoltage increase as a function of time of various trace compounds of different concentration in different electrolytic media in other successful tests:

operated with a fixed voltage of 0.95 v., it was found that trace concentration variations of from 10 to dodecylbenzene sulfonate produced detectable changes with a rate of change, representing rate of variation in over- Trace Hydrogen overvoltage increase increase (mv.) ln

Supporting electrolyte Trace compound concentration 1 min. 3 min. 5 min.

Proteins:

0.1 N H2804 Egg albumin. 1 ppm 18 64 110 0 1 do 0.01 p.p.m 14 20 34. 0.1 N H280 do 0.001 p.p.m 8 21 23 0.1 N H2504 Calf thymus hlStOllQ..- 0.01 ppm 20 56 0.1 N 280.; (pl-I 5.5) d0 0.1 p.p.m S 20 0.1 N K280 (pH 5.5) Choline csterase (1%)- 0.1 p.p.m. (10 17 21 p.p.m. others). 0.1 N 11:80; E. Coli (frozen and 2 p.p.m 24

reheated bacteria). Other model compounds:

0.1 N H 80, Dodccylbenzyldi- 10-6 molar 23 33 methylammoninm chloride. 0.1 N H280 Sodium stearate 10- molar 11 26 It is to be understood that, while the invention is particularly useful for the detection of intermediate and high molecular weight organic compounds, the techniques underlying the invention are equally applicable for the detection of other types of traces, all herein termed chemical agents, including bacteria and the like in urine, blood, and other types of electrolytic media.

Extremely sensitive operation, moreover, has been found possible when the electrolytic medium is pro-electrolyzed to remove impurities and to increase the desired ion concentration, such as, for example, hydrogen in the case of hydrogen overvoltage detection in the main cell. Such operation is shown effected in the drawing by connecting the electrolyte reservoir 17 to a pre-electrolyzing cell of preferably U-shape construction having an anode 30 disposed in the left-hand arm of the U and a cathode 50 disposed therebelow in the right-hand arm of the U. The electrolytic medium is shown introduced adjacent the cathode 50, and it is pre-electrolyzed by the passing of current from the source B with anolyte waste ejected from outlet 90 near the anode 30, and purified electrolyte with dissolved hydrogen fed from outlet 92 to the beforementioned inlet 7 of the cell 1. The outlet 92 is preferably larger than and lower in position than the outlet 90 to insure the desired output from the pre-electrolysis cell, and the lower portion of the left-hand leg of the cell below the anode 30 is preferably sintered, as at 31, to prevent feedback from the right-hand arm of the cell. Clearly, other types of pre-electrolysis cell constructions may readily be employed.

As previously stated and as indicated in the table above, correlation between the slope of the overvoltage characteristic C and the quantity of the trace concentration has been found. Absolute measurement of this slope and thus of the rate of overvoltage increase or other variation may be read at 15', particularly if the voltage of the test cell cathode 5 is normalized or compared diiferentially at 15 with respect to the overvoltage of a standard cell 1 receiving the same electrolytic medium but absent the trace concentrations. This is shown effected with the aid of a standard comparison cell 1' shown constructed in the same manner as the test cell 1 and receiving the same electrolyte from the outlet 92, the various constructional parts of the comparison cell 1' being given the same numbering as the corresponding parts of the test cell 1, although with a prime notation.

While the invention has been described in connection with hydrogen overvoltage measurements, it is to be understood that it is more generally applicable, also, to overvoltage measurements of other ions developed at an electrode in an electrolysis cell of this character. As a further example, the rate ofincrease of oxygen overvoltage at an anode with trace concentration has also been observed. In a cell containing 0.1 N NaOH electrolyte voltage, of approximately 10- amps/second produced over a period of approximately 3 seconds after addition of the trace compound. It is to be understood that whether the rate of variation in overvoltage is measured by measuring voltage change or current change is immaterial to the underlying principles of operation of the method of the present invention.

While the technique of the present invention can well be employed with closed cell structures on a batch principle basis, it is preferred to use the flow-through system as described in connection with the cells 1 and 1' because this automatically introduces agitation that insures uniformity of trace concentration at the desired electrode and also permits the construction of the test cell in very miniature form. Clearly, other types of agitation may be effected to insure unform concentration of the trace compound in the region of the sensing electrode.

It has also been discovered that, following measurements of the above-described character, the sensing electrode, such as the cathode 5, with adhered trace compound, may be regenerated by removing the traces to enable subsequent independent measurements of rate of overvoltage variation. Such regeneration has been effected by reversing the potential and current applied between the electrodes for a short period of time. This may be readily done by operating the switch S to make contact with the reverse-polarity voltage source B in the cell 1 and/or in the cell 1.

Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A method of detecting traces of foreign chemical agents in an electrolytic medium containing anodic and cathodic electrodes, that comprises, connecting a voltage source external of said medium between said electrodes, passing current from said source between the electrodes through said medium to electrolyze the electrolytic medium, discharging ions of the medium at the electrodes in response to said current, generating a gas at one of said electrodes in response to said discharging of ions thereat, producing an overvoltage at said one electrode dependent upon the generation of said gas, introducing into the medium traces of said agents and effecting corresponding increases in said overvoltage and in the polarization at said on! of the electrodes, measuring the rate of increase in overvoltage at the said one electrode and determining from such rate the quantity of such traces.

2. A method as claimed in claim 1 and in which the medium is agitated in the region of said one electrode.

3. A method as claimed in claim 2 in which the agitation comprises causing the medium to flow past said one electrode.

4. A method as claimed in claim 1 and in which the further step is performed of reversing the direction of current passage between the electrodes to regenerate said one electrode for enabling subsequent independent measuring of the rate of overvoltage variation.

5. A method as claimed in claim 1 and in which the electrolytic medium is pre-electrolyzed prior to the said current passing step.

6. A method as claimed in claim 1 in which said agents are intermediate or high molecular weight organic compounds and in which said electrolytic medium is an aqueous solution.

7. A method as claimed in claim 6 in which said compounds are nitrogen-containing.

8. A method as claimed in claim 1 in which the said medium is acidic.

9. A method as claimed in claim 1 in which the said medium is basic.

10. A method as claimed in claim 1 and in which the last-mentioned step comprises electrolyzing a sample of the said electrolytic medium absent the traces of said agents between a further pair of said electrodes, and comparing the resulting overvoltage at an electrode of said further pair with that produced at the said one electrode.

11. A method as claimed in claim 1 and in which the said electrolytic medium is an acidic solution, the said one electrode is cathodic and the said ions discharged thereat are hydrogen.

12. A method as claimed in claim 1 and in which the said agents are bacteria.

References Cited UNITED STATES PATENTS 943,188 12/1909 Hartman 204149 2,786,021 3/1957 Marsh 204--1.1 3,275,534 9/1966 Cannon et a1 2041.1 3,296,113 1/1967 Hansen 204l 3,315,270 4/1967 Hersch 204l95 1,956,411 4/1934 Bonine 204149 2,744,061 5/ 1956 De Ford et a1 204l95 2,886,496 5/ 1959 Eckfeldt 204l95 3,154,477 10/ 1964 Kesler 204l95 3,403,081 9/1968 Rohrback et al. 2041.1 3,005,758 10/ 1961 Spracklen et a1 204l95 3,038,848 6/1962 Brewer et a1 204l95 3,479,255 11/1969 Arthur 2041.1

OTHER REFERENCES Malmstadt et al.: Analytical Chem., vol. 33, No. 8, July 1961, pp. 1040-1047.

Kramer et al.: Analytical Chem, vol. 34, No. 7,

June 1962, pp. 842-845.

Guilbault et al.: Analytical Chem, vol. 34, No. 11,

October 1962, pp. 1437-1439.

TA-HSUNG TUNG, Primary Examiner US. Cl. X.R. 204l95 

